In order to protect the cell area and in order to ensure a permissible blocking voltage for the switching structures which are arranged in the cell area, a protection electrode is arranged around the cell area in conventional semiconductor components and is at the lowest potential in the circuit during operation of the semiconductor part.
A semiconductor component having a drift path and at least one ring electrode as an edge termination is described in Patent Application DE 10 2005 023 026.1. For this purpose, not only a single ring electrode but a multiplicity of field rings of a second, complementary conductance type, are arranged as an edge termination in the edge area of a first conductance type of the semiconductor body.
The document U.S. Pat. No. 6,274,904 B1 also relates to an edge structure of a semiconductor component, with a semiconductor body of a first conductance type having an edge area with a multiplicity of areas of the complementary conductance type, which are arranged on two levels. These areas are electrically connected or capacitively coupled to one another.
Furthermore, the document U.S. Pat. No. 6,621,122 B2 discloses a termination structure in which a field ring, which is an extension of the source electrode, forms the termination at a radial center point of the termination area, with an active surface being surrounded by the termination area, which has columns of different shape of a complementary conductance type to the drift path.
Known edge termination structures such as these are intended to ensure that the breakdown voltage that is intended for that component is also achieved in the edge area. A further aim is for an edge termination structure to ensure electrical isolation between monolithically adjacent components or, in the case of components positioned in the border, electrical isolation towards an edge of the semiconductor chip.
One disadvantage of the edge termination structures described in the above documents is that the pn junctions which are arranged in the edge area have curvatures between a first and a complementary conductance type, which lead to an increase in the electrical field in the area of the curvature, and to a reduction in the breakdown voltage. Furthermore, the above structures in the form of capacitively coupled field rings, field plates and/or edge terminations with semiconductive layers occupy a large amount of space.
The disadvantage of the large amount of space that is occupied can be overcome by means of oxide-filled ring trenches, as are described in Patent Application DE 10 2004 041 892. Ring trenches such as these which surround the cell area of the semiconductor components can decrease the blocking voltage on a considerably shorter path, owing to the higher breakdown field strength of the oxide in comparison to that of silicon.
However, FIG. 7 shows the disadvantage of an oxide-filled ring trench 25 such as this if, for example, it has an adequate width b, which in this case is between 3 and 4 micrometers, with the ring trench 25 extending to a depth t of about 45 micrometers into the drift path 4 of the semiconductor body 5. With a minimal width b such as this, a hole channel 24 is formed even at 240 V on that side 23 of the oxide-filled ring trench 25 which faces away from the cell area 8, and this hole channel 24 contains the breakdown charge which is required to dissipate the electrical field, and thus prevents any further decrease in voltage in the semiconductor material.
A ring trench structure therefore has the disadvantage that it is necessary to dissipate all of the voltage in a sufficiently broad oxide-filled first ring trench 25 because the maximum voltage which can be dissipated in the situation shown in FIG. 7 is restricted to 240 V if the width of the first ring trench 25 or of the innermost ring trench 25 is not adequate. Even a plurality of oxide-filled ring trenches arranged in a stack form towards the edge do not make any additional contribution, and can therefore not increase the voltage which can be dissipated.